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The Evolution of Medical Human Body Temperature Measuring Instruments

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The Evolution of Medical Human Body Temperature Measuring Instruments

   In 1593, the Italian scientist Galileo invented the world’s first thermometer. It used a glass flask with a very thin neck. The bottle contained half of the colored water. Put it upside down and put it in a bowl. With the same color of water, as the temperature changes, the air contained in the bottle will shrink or expand, and the water column in the neck will rise or fall. In 1632, the French physicist Rey was the first to improve Galileo’s thermometer. He turned Galileo’s device upside down and injected water into the glass bulb while leaving air in the glass tube, still expressed by the height of the water column in the glass tube. The temperature is high and low, because of this improvement, water becomes a temperature measuring substance. In 1714, the Dutch scientist Wallenheit changed the temperature-sensitive liquid to mercury and produced the first practical mercury thermometer. At the same time, the Fahrenheit temperature scale was established. However, due to its large size and inconvenience, it was not widely used by doctors. Until 1865, the British Albert invented a glass thermometer with a special structure. The structure of this thermometer is characterized by a narrow channel between the temperature-sensitive bubble that stores mercury and the thin tube. When the thermometer touches the human body, the mercury rises to the actual body. When the body temperature is taken out, the mercury column drops and the narrow channel is disconnected so that the upper part of the narrow channel always maintains the body temperature. This kind of thermometer is popular and popular in clinical practice. The medical human body temperature measuring instrument was born and is still in use today.

   Around the 1970s, with the rapid development of electronic information technology, in addition to traditional mercury thermometers, measuring instruments such as electronic thermometers, infrared forehead thermometers and infrared thermal imaging cameras appeared in clinical practice.

1. Mercury thermometer

   The structure of the mercury thermometer is mainly composed of a temperature-sensitive bubble containing mercury, a glass capillary tube and a graduated scale. The temperature measurement principle of thermal expansion and contraction is adopted. When the mercury in the bubble is affected by body temperature, it will expand, causing the mercury column in the tube to expand. The length has changed significantly. When the temperature measurement of the human body reaches equilibrium, the mercury column is constant, thereby achieving the measurement purpose.

2. Electronic thermometer

   The electronic thermometer is mainly composed of a temperature sensor, a thermometer, a display screen, a switch button, and a battery. The electronic thermometer uses a temperature sensor to output electrical signals, and then displays them in digital form through a display (such as liquid crystal, digital tube, LED matrix, etc.) It can record and read the highest temperature of human body. The core component of an electronic thermometer is a temperature sensor that senses temperature.

3. Infrared Forehead Thermometer

   The basic working principle of the infrared forehead thermometer is that all objects with a temperature higher than absolute zero will emit a certain proportion of infrared radiation energy according to their own temperature. The size of the radiation energy and the distribution of its wavelength are closely related to the surface temperature of the object; so According to this principle, an infrared forehead thermometer can obtain human body temperature measurement data by measuring the infrared radiation of the human forehead, then convert this signal into a temperature signal, and finally perform forehead temperature compensation to calculate the real body temperature of the human body.


Figure 1. Infrared thermal image.

4. Thermal imaging camera

   Infrared thermal imaging camera converts the spatial distribution of the surface temperature of the target object into a temperature distribution map that can be perceived by human sight. In general, it converts the invisible infrared energy emitted by the object into a visible thermal image. The color on the thermal image represents the measured temperature. Different temperatures of objects. By viewing the infrared thermal image, you can observe the overall temperature distribution of the measured target, and study the heating of the target in order to make the next work judgment. The basic principle is to use an infrared detector and an optical imaging objective lens to receive the infrared radiation energy distribution pattern of the measured target and reflect it on the photosensitive element of the infrared detector to obtain an infrared thermal image.

   Due to the frequent occurrence of fever and infectious diseases, a large number of people need to be tested for body temperature, so the mercury thermometer cannot meet the demand during use. Therefore, using the principle of self-service, the infrared thermal imaging camera was invented to reduce mechanical and repetitive manual intervention. After only installing the infrared thermal imaging camera and aiming at the measured object, the measurement results can be directly displayed, which enhances the measurement efficiency.


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